The present invention relates to a method for finishing a surface of a work by electrolytic machining, and more particularly to a method for accurately controlling the machining depth.
Japanese Patent Application Laid-Open 63-114815 discloses a method for finishing a work machined by electrolytic machining. In the method, the work which is secured in an electrolyte tank is positioned to form a predetermined gap between an electrode and the surface of the work. A pulse is applied to the electrode in stationary liquid electrolyte, and then clean electrolyte is intermittently supplied to the gap, discharging the electrolyte including residual products.
In the method, a desired machining depth of the work necessary to obtain the required surface roughness of the work without deteriorating the roughness obtained through the electrolytic machining is calculated in dependency on data acquired by experiments and trials. The quantity of coulombs required to machine a unit of area to a desired machining depth is calculated based on an equation which relates the electrochemical equivalent for the particular work material and the current efficiency determined by experiments.
If the machine finishing is carried out under the same conditions as the experiments, the dimensions of the finished surface is in a small range within +5% of the desired dimensions. However, owing to the difference of the concentration, temperature and pH of the electrolyte from that of the experiment, it is difficult to machine the work under the same conditions, Moreover, the shape of the surface of the work is too complicated to accurately calculate the surface area thereof, causing an error in the calculation. The error affects the calculation of the quantity of coulomb per area unit, so that the machining accuracy is impaired.
In addition, it is difficult to flush the liquid electrolyte through the gap between the work and the electrode in the same manner as the experiments. As a result, residual products in the gap cannot be effectively and uniformly removed, deteriorating machining efficiency, particularly so in a work with a complicated surface. Thus, the actually machined depth becomes smaller than the desired depth, and hence it is impossible to produce accurate products.